Method for controlling powder compacting apparatus and compacting apparatus

ABSTRACT

There is provided a method for controlling a powder compacting apparatus including: a die having a hollow; an upper punch; a floating lower punch; a first actuator that pushes down the upper punch; a second actuator that controls a floating load of the floating lower punch; and a stopper that defines a pressurization stop position of the floating lower punch. The powder compacting apparatus is configured such that the first actuator is operated to push down the upper punch to pressurize powder charged into the cavity, and the second actuator is controlled to pressurize the powder such that a load acting on the powder during pressurization becomes a prescribed floating load required to compact the powder. The method includes causing the first actuator to reduce a descending speed of the upper punch when the floating lower punch reaches a position at a prescribed distance from the stopper.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2015-198617 filed on Oct. 6, 2015 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The disclosure relates to a method for controlling a powder compacting apparatus, and relates also to a compacting apparatus.

2. Description of Related Art

One of the methods for compacting powder under pressure is a float compacting method. The float compacting method is carried out by using a powder compacting apparatus that mainly includes a die having a hollow, a floating lower punch that slides in the hollow, an upper punch that is also slidable in the hollow, and various actuators that respectively drive the floating lower punch and the upper punch.

Powder is charged into a cavity defined by the die, the floating lower punch, and the upper punch. Then, the powder is pressurized by pushing down the upper punch by using an actuator, such as a hydraulic cylinder or an air cylinder. At this time, the powder is pressurized while the floating lower punch is slid by an actuator such that a prescribed pressurizing force (floating load) acts on the powder. There is also a powder compacting apparatus in which a stationary lower punch that does not slide is disposed around a floating lower punch, and a cavity is defined by the stationary lower punch, the floating lower punch, a die, and an upper punch.

There is also a powder compacting apparatus configured such that, in addition to a floating lower punch and an upper punch, a die can also be slid by an actuator. In the thus configured powder compacting apparatus, the upper punch and the floating lower punch pressurize powder while descending at prescribed respective rates (speeds). At this time, for example, while the upper punch is descending at a speed of 10 and the floating lower punch is descending at a speed of 7, the die is also descending, for example, at a speed of 8. With this configuration, when the powder is gradually compacted from the vicinity of the upper punch to produce a green compact, it is possible to inhibit the generation of a density distribution in which the density of the green compact decreases with increasing proximity to the upper punch (i.e., a density distribution in which the density of the green compact becomes lower as the distance to the upper punch decreases in the green compact).

In the float compacting method, there may be executed a control in which pressurization by the upper punch and the floating lower punch is completed upon the lapse of a prescribed period of time after the floating lower punch that descends reaches a stopper.

SUMMARY OF THE DISCLOSURE

In such a control, the floating lower punch continues to descend (continues an attempt to descend) during a control period required to stop the descending of the floating lower punch. Therefore, when the period of time until the stop of the floating lower punch is long, the motion of the floating lower punch that is prevented from further descending by the stopper and that attempts to continue descending, may be propagated to the entirety of the powder compacting apparatus. This may lead to damages to the powder compacting apparatus.

This will be described with reference to FIG. 5 illustrating an upper punch and floating lower punch displacements versus time graph and a floating lower punch load versus time graph. The floating lower punch during pressurization has a descending speed generated by the actuator. Thus, a floating load starts decreasing at the moment when the floating lower punch reaches the stopper. When there is sufficient time required for the control, the rotational speed of the actuator that has operated the floating lower punch in the descending direction starts to be reduced in order to maintain the decreased floating load at a set value. After the descending speed of the floating lower punch becomes zero, the floating lower punch is actuated toward the ascending side until a floating load is obtained.

The time required for control is limited. Therefore, when the descending speed of the floating lower punch immediately before the floating lower punch reaches the stopper is high, the control for appropriately maintaining the floating load cannot be carried into effect. As a result, the floating load of the floating lower punch is sharply decreased, as illustrated in FIG. 5.

When the floating load acts in a tensile direction, components of the powder compacting apparatus may be pulled downward. This may lead to damages to the powder compacting apparatus.

Japanese Patent Application Publication No. 06-25706 (JP 06-25706 A) describes a powder compacting apparatus. In the powder compacting apparatus, a die is movably disposed in a die holder that operates along with a press lower ram, a stationary lower punch and a floating lower punch are disposed on a punch plate of which the position is fixed, the floating lower punch is supported by a cylinder device incorporated in the punch plate, and one end of a connecting rod that operates along with the press lower ram is disposed in a bore of the cylinder device. Powder is held between the floating lower punch and a floating upper punch, and is partially displaced. Then, a piston of the cylinder device is brought into contact with the connecting rod, thereby applying an ascending force of the press lower ram to the powder, so that pre-compacting is performed. Subsequently, the descending of the floating lower punch is stopped by a stopper, and final compacting is performed.

With the powder compacting apparatus described in JP 06-25706 A, using the press lower ram contributes to size reduction and simplification of a powder transport mechanism. However, even when the powder compacting apparatus described in JP 06-25706 A is employed, there is still the aforementioned problem, that is, there is still a possibility that the floating lower punch will reach the stopper with a descending speed and the floating load will be sharply decreased, leading to damages to the powder compacting apparatus.

The disclosure is made to address the aforementioned problem, and the disclosure provides a method for controlling a powder compacting apparatus and a compacting apparatus, the method and the compacting apparatus allowing reduction in the possibility of causing damages to the powder compacting apparatus due to a sharp decrease in a floating load, by shortening, as much as possible, a period of time from when a floating lower punch reaches a stopper until when the floating lower punch completely stops a motion of attempting to further descend.

A first aspect of the disclosure relates to a method for controlling a powder compacting apparatus including at least: a die having a hollow; an upper punch and a floating lower punch that slide in the hollow, the upper punch and the floating lower punch defining a cavity along with the die; a first actuator that pushes down the upper punch; a second actuator that controls a floating load of the floating lower punch; and a stopper that defines a pressurization stop position of the floating lower punch, the powder compacting apparatus configured such that the first actuator is operated to push down the upper punch to pressurize powder charged into the cavity, and the second actuator is controlled to pressurize the powder such that a load acting on the powder during pressurization becomes a prescribed floating load required to compact the powder. The method for controlling the powder compacting apparatus includes causing the first actuator to reduce a descending speed of the upper punch when the floating lower punch reaches a position at a prescribed distance from the stopper.

A second aspect of the disclosure relates to a compacting apparatus. The compacting apparatus includes: an upper punch driven by a first actuator; a floating lower punch disposed below the upper punch, and the floating lower punch being driven by a second actuator to pressurize an object along with the upper punch; and a stopper that defines a stop position of the floating lower punch. The first actuator reduces a driving speed of the upper punch when the floating lower punch reaches a position at a prescribed distance from the stopper.

There is provided a method for controlling a powder compacting apparatus including a die having a hollow; an upper punch and a floating lower punch that slide in the hollow, the upper punch and the floating lower punch defining a cavity along with the die; a first actuator that pushes down the upper punch; a second actuator that controls a floating load of the floating lower punch; and a stopper that defines a pressurization stop position of the floating lower punch. The method for controlling the powder compacting apparatus includes: charging powder into the cavity; controlling the first actuator and the second actuator such that a load acting on the powder becomes a prescribed floating load; and causing the first actuator to reduce a descending speed of the upper punch when the floating lower punch reaches a position at a prescribed distance from the stopper.

In the above aspects, the first actuator is controlled to reduce the descending speed of the upper punch when the floating lower punch reaches the position at the prescribed distance from the stopper. Thus, it is possible to shorten, as much as possible, a period of time from when the floating lower punch reaches the stopper until when the floating lower punch completely stops a motion of attempting to further descend.

During float compacting, a control for causing the floating lower punch to descend while the upper punch is descending is executed. When the descending speed of the upper punch is reduced, the floating lower punch is controlled such that the descending speed of the floating lower punch is also reduced in accordance with the reduction in the descending speed of the upper punch. With this control, by controlling the timing at which the descending speed of the upper punch is reduced, it is possible to shorten a period of time from when the floating lower punch reaches the stopper until when the floating lower punch is completely stopped.

The position of the floating lower punch relative to the stopper is determined by the second actuator.

When it is determined by the second actuator that the position of the floating lower punch reaches the position at the prescribed distance from the stopper, the control for reducing the descending speed of the upper punch by the first actuator is executed based on this information.

In the above aspects, each of the first actuator and the second actuator may be a servo actuator.

The “prescribed distance” from the stopper to the position reached by the floating lower punch is a distance that corresponds to the start of reduction in the descending speed of the upper punch, with which the floating load is not sharply decreased during a period from when the floating lower punch reaches the stopper until when the pressurization is completed. The “prescribed distance” is set in consideration of, for example, the speed of the upper punch after speed reduction, the time required for speed reduction of the upper punch, the distance over which the floating lower punch descends during speed reduction of the upper punch, and the amount of elastic deformation of the floating lower punch.

According to the disclosure, the distance from the stopper to the floating lower punch is used as a trigger for the start of reduction in the descending speed of the upper punch, and the timing at which the descending speed of the upper punch is reduced is controlled based on the trigger. Thus, a sharp decrease in the floating load can be avoided, and damages to the powder compacting apparatus due to a sharp decrease in the floating load can be effectively avoided.

As can be understood from the above description, in the method for controlling the powder compacting apparatus according to the disclosure, the first actuator that pushes down the upper punch is controlled to reduce the descending speed of the upper punch when the floating lower punch reaches the position at the prescribed distance from the stopper. Thus, a sharp decrease in the floating load after the floating lower punch reaches the stopper is prevented, and damages to the powder compacting apparatus due to a sharp decrease in the floating load can be effectively avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic view illustrating a state where powder has been charged into a cavity of a powder compacting apparatus to which a controlling method of the disclosure is applied;

FIG. 2 is a schematic view illustrating a state where the controlling method of the disclosure is carried out to pressurize the powder, thereby forming a green compact;

FIG. 3 is a schematic view illustrating a state where a floating lower punch reaches a stopper;

FIG. 4 is a diagram illustrating an upper punch and floating lower punch displacements versus time graph and a floating lower punch load versus time graph, both of which illustrate the controlling method of the disclosure; and

FIG. 5 is a diagram illustrating an upper punch and floating lower punch displacements versus time graph and a floating lower punch load versus time graph, both of which illustrate a conventional controlling method.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a method for controlling a powder compacting apparatus according to an example embodiment of the disclosure will be described with reference to the accompanying drawings.

Method for Controlling Powder Compacting Apparatus According to Embodiment

FIG. 1 is a schematic view illustrating a state where powder has been charged into a cavity of a powder compacting apparatus to which a controlling method of the disclosure is applied. FIG. 2 is a schematic view illustrating a state where the controlling method of the disclosure is carried out to pressurize the powder, thereby forming a green compact. FIG. 3 is a schematic view illustrating a state where a floating lower punch reaches a stopper. FIG. 4 is a diagram illustrating an upper punch and floating lower punch displacements versus time graph and a floating lower punch load versus time graph, both of which illustrate the controlling method of the disclosure.

A powder compacting apparatus 10 illustrated in the drawings mainly includes a die 1 having a hollow 1 a, a third actuator 2 that slides the die 1 (in a direction X3), an upper punch 3 that slides in the hollow 1 a, a first actuator 4 that slides the upper punch 3 (in a direction X1), a stationary lower punch 6 that is partially disposed in the hollow 1 a, a floating lower punch 5 that slides in the stationary lower punch 6, a second actuator 7 that slides the floating lower punch 5 (in a direction X2), and a stopper 8 on which the stationary lower punch 6 is disposed, the stopper 8 defining a descending limit of the floating lower punch 5.

Each of the first actuator 4, the second actuator 7, and the third actuator 2 is constituted by an electric servomotor.

In the powder compacting apparatus 10, during float compacting, a control for causing the floating lower punch 5 to descend (in the direction X2) while the upper punch 3 is descending (in the direction X1) is executed, so that a floating load is applied to powder F due to the descending of the floating lower punch 5. When the descending speed of the upper punch 3 is reduced, the floating lower punch 5 is controlled such that the descending speed of the floating lower punch 5 is also reduced in accordance with the reduction in the descending speed of the upper punch 3.

This control is feasible because each of the first actuator 4 and the second actuator 7 is constituted by a servo actuator (an electric servomotor).

The die 1 is also caused to descend (in the direction X3) by the third actuator 2 (the electric servomotor) while the floating lower punch 5 and the upper punch 3 are descending. With this configuration, when the powder F is gradually compacted from the vicinity of the upper punch 3 to produce a green compact C (see FIG. 3), it is possible to inhibit the generation of a density distribution in which the density of the green compact C decreases with increasing proximity to the upper punch 3 (i.e., a density distribution in which the density of the green compact C becomes lower as the distance to the upper punch 3 decreases in the green compact C).

As illustrated in FIG. 1, a cavity is defined by an inner peripheral surface of the die 1, which defines the hollow 1 a, an upper surface of the floating lower punch 5, and an upper surface of the stationary lower punch 6. The powder F to be compacted is charged into the cavity.

Next, as illustrated in FIG. 2, the powder F is pressed downward while the upper punch 3 is descending to apply a pressing force P to the powder F. While the upper punch 3 is descending, the floating lower punch 5 is also caused to descend, thereby applying a floating load P′ to the powder F. The descending control of the upper punch 3, the floating lower punch 5, and the die 1 is executed while the floating load P′ acts on the powder F.

When pressurization of the powder F proceeds and the floating lower punch 5 reaches a position at a prescribed distance from the stopper 8 (see (1) in FIG. 4), a command signal for reducing the descending speed is transmitted from the second actuator 7 to the first actuator 4 that controls the descending speed of the upper punch 3 (see (2) in FIG. 4).

The “prescribed distance” is set in consideration of, for example, the speed of the upper punch 3 after speed reduction, the time required for speed reduction of the upper punch 3, the distance over which the floating lower punch 5 descends during speed reduction of the upper punch 3, and the amount of elastic deformation of the floating lower punch 5.

Reduction in the descending speed of the upper punch 3 is started under the control by the first actuator 4 that has received the command signal (see (3) in FIG. 4), and the second actuator 7 executes a control for reducing the descending speed of the floating lower punch 5 such that a certain floating load is maintained, based on the reduction in the descending speed of the upper punch 3.

The descending speeds of the upper punch 3 and the floating lower punch 5 are gradually reduced, and then the floating lower punch 5 with a low descending speed reaches the stopper 8 (see (4) in FIG. 4).

The floating load is moderately decreased (see (6) in FIG. 4) during a period from when the floating lower punch 5 reaches the stopper 8 until when the pressurization is completed (see (5) in FIG. 4).

Upon completion of the pressurization, the green compact C having a prescribed shape is obtained, as illustrated in FIG. 3.

According to the controlling method illustrated in the drawings, when the floating lower punch 5 reaches a position at a prescribed distance from the stopper 8, the first actuator 4 is controlled to reduce the descending speed of the upper punch 3. In this way, a sharp decrease in the floating load as in the conventional controlling method illustrated in FIG. 5 can be avoided.

Because a sharp decrease in the floating load can be avoided, damages to the apparatus due to a sharp decrease in the floating load can be avoided.

While the embodiment of the disclosure has been described in detail with reference to the drawings, the specific configuration is not limited to the foregoing embodiment, and the disclosure is intended to cover various design changes or the like within the scope of the disclosure. 

What is claimed is:
 1. A method for controlling a powder compacting apparatus including at least: a die having a hollow; an upper punch and a floating lower punch that slide in the hollow, the upper punch and the floating lower punch defining a cavity along with the die; a first actuator that pushes down the upper punch; a second actuator that controls a floating load of the floating lower punch; and a stopper that defines a pressurization stop position of the floating lower punch, the powder compacting apparatus configured such that the first actuator is operated to push down the upper punch to pressurize powder charged into the cavity, and the second actuator is controlled to pressurize the powder such that a load acting on the powder during pressurization becomes a prescribed floating load required to compact the powder, the method comprising causing the first actuator to reduce a descending speed of the upper punch when the floating lower punch reaches a position at a prescribed distance from the stopper.
 2. The method for controlling the powder compacting apparatus according to claim 1, wherein each of both the first actuator and the second actuator is an electric servomotor.
 3. A compacting apparatus comprising: an upper punch driven by a first actuator; a floating lower punch disposed below the upper punch, and the floating lower punch being driven by a second actuator to pressurize an object along with the upper punch; and a stopper that defines a stop position of the floating lower punch, wherein the first actuator reduces a driving speed of the upper punch when the floating lower punch reaches a position at a prescribed distance from the stopper.
 4. A method for controlling a powder compacting apparatus including a die having a hollow; an upper punch and a floating lower punch that slide in the hollow, the upper punch and the floating lower punch defining a cavity along with the die; a first actuator that pushes down the upper punch; a second actuator that controls a floating load of the floating lower punch; and a stopper that defines a pressurization stop position of the floating lower punch, the method comprising: charging powder into the cavity; controlling the first actuator and the second actuator such that a load acting on the powder becomes a prescribed floating load; and causing the first actuator to reduce a descending speed of the upper punch when the floating lower punch reaches a position at a prescribed distance from the stopper. 